7.65 Argentine. It was the first cartridge I ever reloaded, cutting down .30-06 brass, trimming it with the file die, swaging the shoulder back, etc. Back in the mid-1980s there was no 7.65 brass to be had anywhere.
Same situation for the Star Super I got shortly afterward, chambered in 9mm Largo. I cut the rims off .38 Special in the lathe and cut extractor grooves in the bases.
Now I'm set up for .44 AMP, and will be doing .30 Remington soon.